Circuitry Underlying Visual Processing in the Retina
Early retinal processing is involved with managing the set point for retinal neurons, taking care to keep all neural activity of each cell at a neutral set point, about midway between its maximal and minimal activity levels. Most retinal neurons are active at their midpoint, receiving and transmitting even under ambient conditions. Light input alters the patterns of activity among these neurons.
There is a general organizational plan for the inner retina whereby vertically oriented inhibition is carried by a population of many different amacrine cell types, defined by morphology. Many of these amacrine cells are narrowly diffuse glycinergic amacrine cells. For the most part these vertical cells carry information from the ON to the OFF systems, and provide “crossover inhibition” that serves to correct for the rectification inherent in all synapses. Wide field inhibition is carried by laterally oriented GABAergic amacrine cells. This inhibition forms a second tier of antagonistic interaction. Wide field inhibition is mediated by at least five different antagonistic surround possibilities: Horizontal cell feedback, horizontal cell GABA and electrical feedforward, GABAergic wide amacrine cell feedback, GABAergic wide amacrine cell feedforward, and glycinergic amacrine cell crossover inhibition. In addition to the general plan, there are specific circuitries that account for the unique behavior of individual ganglion cell types. A few examples of this specific circuitry are now available, and have been described above near the end of this chapter.
KeywordsGanglion Cell Bipolar Cell Amacrine Cell Cone Bipolar Cell Starburst Amacrine Cell
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